Basement remodel – existing insulation
What a great forum–just found it the other day and have spent hours on it already!
I’m planning to finish the walk-out basement in my 2-year old spec house. Three walls are poured concrete, and these walls are covered with a fairly thin blanket of fiberglass insulation w/vapor barrier that’s powder-nailed to the concrete walls (the basement is heated & cooled already). Looks like a big padded room (which I may need as I get farther along in this). I’m planning on building stud walls to overlay the concrete walls, as floor space isn’t a problem.
My question is: should I rip out all this existing insulation, then build the new walls 1″ or so away, and install all new insulation & vapor barrier in the stud cavities? Or should I leave the insulation, and build the new walls say 4″ away from the concrete to avoid compressing the existing insulation? My thinking is that everything seems to work pretty well now, i.e. basement stays comfortable in summer & winter, no moisture problems, so should I be fixing it if it ain’t broke?
Thanks in advance,
Mike Powell
Replies
If you've been observing this site, you probably know what a "bump" is. If you don't, that's what this will be--moves your post up near the top without giving an answer.
I am having trouble picturing nailed fiberglass insul..Normally I glue polystyrene to the wall and frame in front of that. Nailing the fiberglass will compress it and therefore will not work the best that it can. But like you said if it ain't broke, just frame in front, sheetrock; leave a gap at the floor, and go on from there, use a piece of pressure treated lumber for the base plate. Keep in mind that you may get numerous other suggestions, some good some not.
Thanks for the reply--I didn't describe the existing insulation very well. I think it's pretty common in spec houses around here (central VA); at least I've seen it in other houses. It's 3-4" of fiberglass, with a backing facing the inside that appears to be some kind of fiber-reinforced plastic, and it's installed horizontally in long 4' wide strips. The nails that hold it on have big plastic washers built into them, and they do compress the insulation like you said.
I'm not sure from your description, but I think you're talking about a type of compressed fibreglas panel that we have occasionally used in the past for exterior insulation. This material is quite dense, but it is not hard or rigid. If it is nailed on directly, it would certainly require washer-head nails.
In an exterior installation, this material is laid onto the sheathing and then held in place with 1x strapping--which is nailed through the FG panels to the sheathing and studs (and it's fun finding the studs, I can tell you!)--to which the siding is finally nailed. The 'fibre-reinforced plastic' that you spoke of sounds like the integral vapour barrier that's on one side of these panels.
If that is indeed what you've got on your basement walls, you could save yourself the cost of framing complete stud walls and just install top and bottom plates--interior edges flush with the interior face of the FG--then strap over the fibreglass and onto the plates. You'd probably be best advised to attach the strapping with long Tap-Cons and be careful to drive them as uniformly as possible (so as not to compress the panels and bow in the strapping). That could be a touchy part of this process. Once your strapping is up, you can hang your gyprock from the strapping. In that the wall is completely non-structural, and that those pressed FG panels are fairly dense, this 'minimalist' approach would get you finished walls at a fairly low cost.
OTOH, there are advantages in framing a 2x4 stud wall in front of it, too. Not the least of which is the additional wall thickness for insulation that this will provide. I don't know what kind of temps you're dealing with in your area, but if insulation is a major concern, this would probably be a better way to go.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
Dinosaur, thanks for the reply but I still don't think I've described the existing insulation well enough. It is regular soft, squishy fiberglass batting, not dense at all, with a white plasticky backing. In this backing, which faces inside, you can see a grid of fiber reinforcement (like what's in paper packing tape for cardboard boxes) to make it a little stronger than normal paper backing. It appears to have come in 4-foot wide rolls.
Has anyone else seen this stuff? I thought it was not uncommon, but I guess it isn't! I don't see any identifying marks on it. Maybe it's an industrial product--it reminds me of the stuff you might see insulating a steel warehouse or something.
Okay, sorry for veering off on a false trail. I don't have any experience with the specific product you're describing, but it sounds like a variation on single-faced FG batting.
HammerII raises a good point about wicking moisture, though. Because of their high density and great mass, concrete walls are more prone to condensation sweating than framed walls. The concrete will change temperature much more slowly than the air enclosed in that space, hence the conditions necessary for condensation (cold surface, warm moist air) will exist over longer periods of time.
The usual interior insulation used in basements these days is rigid polystyrene panels or gunned urethane foam; these are impervious to moisture and can thus be put in direct contact with the concrete without worrying about the moisture issue. My personal preference is for rigid foam panels; sprayed-on urethane foam has some mechanical inconveniencies attendant on it, as well as being a lot more expensive unless the area being done is quite large.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
Check out this site for lots of advice about how to do it right:
http://www.buildingscience.com
http://www.buildingscience.com/resources/basements.htm
The short version is that you want to tear out the impermeable vapor barrier insulation blanket, install rigid foam on the walls and possibly the floor, and go from there.
Billy
Edited 10/17/2005 1:52 pm ET by Billy
I know what you're describing.
Our general apporach is to remove the blanet foil stuff. Paint all walls with a water proofing paint.
Leave a 1 1/2" air space between the framing and concrete wall. This prevents framing or insulation in the new walls from touching the masonary surfaces and "wicking" water.
If you have a outside enterance for your basement you;ll need to order doors with wider jams or build jam exsitions on site
You might check out the basement finishing article in FHB 169.
Andy Engel
Senior editor, Fine Woodworking magazine
Never try to teach a pig to sing. It wastes your time and annoys the pig.
Other people can talk about how to expand the destiny of mankind. I just want to talk about how to fix a motorcycle. I think that what I have to say has more lasting value. --Robert M. Pirsig
None of this matters in geological time.
Andy Engel's article in FHB, and the Building Science web site are two excellent references.
In addition, you should check w/your local building dept. Some localities have specific requirements that may differ from what you read in the aforementioned sources. This is especially important if you plan on using the space as "living" space, rather than "finished storage space".
Hi,
What did you decide to do with your basement insulation? I'm a little farther north in Virginia and have a basement with the same insulation--fiberglas batts nailed directly to the concrete every few feet, giving the walls a quilted effect. (Which, combined with the foil on the back of the insulation, gives the whole thing a crazy disco vibe). I also assumed we would stud the walls out a few inches from the insulation, but otherwise leave it there.
I decided to stick with my original plan of leaving the existing insulation and building stud walls inside of the batts. A tip if you go this route--remember that you'll need fireblocking under the joists in the 6" or so that's outside of your stud walls. I didn't think of this before putting the walls up so I had to sneak strips of sheetrock in there to close off that path to the joist spaces. This would be easier to do before the walls are in place. :)